The compound (S)-1-{[2-(5-Methyl-2-phenyl-oxazol-4-yl)-ethylamino]-acetyl}-pyrrolidine-2-carbonitrile is useful in the prophylaxis and/or treatment of diseases which are related with the enzyme dipeptidyl peptidase IV (EC.3.4.14.5, abbreviated in the following as DPP-IV). In WO 03/037327, the preparation of (S)-1-{[2-(5-Methyl-2-phenyl-oxazol-4-yl)-ethylamino]-acetyl}-pyrrolidine-2-carbonitrile as well as the uses of this compound have been disclosed. In particular, (S)-1-{[2-(5-Methyl-2-phenyl-oxazol-4-yl)-ethylamino]-acetyl}-pyrrolidine-2-carbonitrile is an inhibitor of DPP-IV and can be used for the treatment and/or prevention of diseases which are associated with DPP-IV, such as diabetes, particularly non-insulin dependent diabetes mellitus, impaired glucose tolerance, bowl disease, colitis ulcerosa, morbus crohn, obesity, and/or metabolic syndrome. The compound can further be used as a diuretic agent or for use as therapeutic active substances for the treatment and/or prophylaxis of hypertension. (S)-1-{[2-(5-Methyl-2-phenyl-oxazol-4-yl)-ethylamino]-acetyl}-pyrrolidine-2-carbonitrile is characterized by formula (I):

Polymorphism is defined as the ability of a substance to crystallize in more than one crystal lattice arrangement. Polymorphism can influence many aspects of solid state properties of a drug. Different crystal modifications of a substance may differ considerably from one another in many respects such as their solubility, dissolution rate and finally bioavailability. An exhaustive treatment of polymorphism in pharmaceutical and molecular crystals is given e.g. by Byrn (Byrn, S. R., Pfeiffer, R. R., Stowell, J. G., “Solid-State Chemistry of Drugs”, SSCI Inc., West Lafayette, Ind., 1999), Brittain, H. G., “Polymorphism in Pharmaceutical Solids”, Marcel Dekker, Inc., New York, Basel, 1999) or Bernstein (Bernstein, J., “Polymorphism in Molecular Crystals”, Oxford University Press, 2002).